There have always been many instances in which liquid chemicals need to be supplied in appropriate volumes to containers from which they are progressively dispensed, while retrieval of the remaining contents after a period of dispensing will in most cases be necessary or desirable. We have found this very pertinent in relation to liquid pre-mix weedicides to be applied by spraying via an agricultural machine, or applied by wick-rope wiping action as in our Australian Patent No. 529361. Whether the liquid chemicals be weedicide or extremely hazardous chemicals, it is obviously desirable that supply and/or retrieval be accomplished with a minimum of spillage since this is harmful to the environment as well as to the operators. Often after a period of use such as at the end of a day, it is necessary to clean pumps and/or other components associated with the distribution containers, thus increasing the risks of spillage. The large number of similar practical applications of this type will be known to users of such equipment or will be apparent from the discussions herein in relation to the present invention.